The invention concerns a method for controlling a blister packaging machine having at least one work station which operates in cycles and performs at least one first adjusting motion for a time period TV1 during one work cycle, assumes a subsequent treatment state for a time period TB in which a product and/or material is/are treated, and performs a second adjusting motion for a time period TV2 which is optionally followed by a resting state for a time period TR, wherein the time periods TV1, TB, TV2 and TR and a resulting cycle rate R (=cycles/min) of the packaging machine are preset and at least the cycle rate R can be changed to a different cycle rate RV using an input means.
A blister packaging machine of conventional structure comprises a forming station, in which a plurality of cup-shaped depressions are formed into a bottom sheet which consists of plastic material or aluminium, into which a product, e.g. a pharmaceutical tablet is inserted in a downstream filling station. After product supply, the bottom sheet is passed to a sealing station. A cover sheet is fed directly before or within the sealing station and disposed on the bottom sheet. The cover sheet is sealed tightly onto the bottom sheet in the sealing station using heat thereby enclosing the product in the cup-shaped depression.
The forming station is operated in cycles and therefore discontinuously. The sealing station can also be operated in cycles or, alternatively, continuously, wherein conventional compensation means effect transfer between cyclical operation of the forming station and continuous operation of the sealing station.
The efficiency of a blister packaging machine mainly depends on the cycle rate R, i.e. the number of cycles to be effected per minute. The cycle rate R defines the maximum cycle time Tmax available for a working cycle in milliseconds with Tmax=60,000/R [ms], i.e. at a cycle rate R of 75 cycles/min, the maximum cycle time Tmax=800 ms. A graph of a corresponding working cycle is shown in FIG. 2 in the form of a simplified polygonal path-time-diagram and is briefly explained below.
The cyclically operated forming station, on which the following example is based, must carry out various motions, treatments, or processes within the maximum cycle time Tmax. Departing from a basic or zero position at the beginning of the cycle (point 0 in FIG. 2), in which two forming plates, between which the bottom sheet to be formed extends, are completely separated, a first adjusting motion, i.e. the closing motion of the forming plates is initially carried out. The closing path sV is defined by the technical production requirements and the closing motion is performed over a predetermined time period TV1 until point 1 (FIG. 2) is reached, at which time the forming plates are closed and have reached their final position.
The forming plates have now assumed their treatment state in which e.g. a pre-heated plastic bottom sheet is cooled for a time period TB, wherein the cup-shaped depressions are additionally formed in the bottom sheet, in particular using compressed air or forming dies. At point 2 of the cycle curve, cooling or treatment of the bottom sheet is completed and is followed by a second adjusting motion, i.e. the opening motion of the forming plates, which is effected again via path SV (however, in the opposite direction) over a time period TV2. At the end of the opening motion, i.e. at point 3 of the cycle curve, the initial position has been reached again. The opened forming plates can subsequently be maintained at a resting state for a time period TR. The duration of the time period TR of the resting state depends mainly on influences external to the forming station and may advantageously be very short or even 0.
As soon as the forming plates are opened to a sufficient degree, further transport of the bottom sheet can be initiated and performed. In FIG. 2, it is assumed that the further transport of the bottom sheet starts when the forming plates have been moved apart by a distance SV/2, i.e. a time period tZ1 is available for further transport of the bottom sheet to the end of the cycle, and a time period tZ2 from the start of the subsequent cycle to the time when the forming plates are again half closed, which produces a total transport time TZ from the sum of tZ1 and tZ2.
In older blister packaging machines, the curve shapes were mechanically defined by rotating cam plates whose rotary motion was derived from a centrally driven main shaft, the so-called king shaft. In modern blister packaging machines, the curves are stored in software and the motor drive of the adjusting motions is effected via servomotors which are controlled by control electronics or corresponding software.
When a blister packaging machine is adjusted to a certain blister format, the motional sections of the cycle curve are usually designed such that they optimally satisfy the process requirements and at the same time can be performed at a maximum cycle rate. The individual cycle steps should thereby be carried out with high reliability and precision and with high efficiency, i.e. high performance of the packaging machine should be obtained. The determined format-specific process data is stored. If the blister packaging machine is to process blisters of the same format at a later time, the stored data is recovered and the packaging machine is correspondingly operated. This process is based on the theoretical idea that the same blister format can always be optimally processed with the same stored process parameters.
Practice has shown that operation of the blister packaging machine which is part of a larger packaging system can cause unexpected problems which reduce the efficiency of the packaging system. These problems may be based on disturbances of individual stations of the blister packaging machine or also disturbances or problems in upstream or downstream systems, e.g. in a downstream cartoning machine. There can be variations in the leaflet material or folding box material in the cartoning machine which would preclude maintaining the preset relatively high cycle rate. Moreover, there could be cycle problems in downstream machines, e.g. in a bundle packer, or product tolerances which have a negative effect on the speed of product supply in the blister packaging machine. In addition, there may be a shortage of staff for the entire packaging system due to illness and/or holidays, with the consequence that the processing speed thereof must be reduced.
Since the above-mentioned problems and disturbances cannot always be eliminated or counteracted immediately, operation of the blister packaging machine is conventionally continued either with an increased rejection rate or reduced packaging quality. If this should not be acceptable, the system is stopped until the cause of the error is eliminated.
In terms of technical control, it would also be possible to reduce the cycle rate of the blister packaging machine and possibly of other machines in the packaging line. This measure could, however, change the forming and sealing parameters to such an extent that perfect forming and sealing processes are no longer guaranteed.
The following is based on an example, wherein the blister packaging machine cannot be operated at an originally preset maximum cycle rate R of e.g. 75 cycles per minute, since the dimensions of the tablets have slightly changed and therefore move at a slightly reduced speed through the supply channels of the filling station. If the cycle rate were not changed, the portion of blisters which are incompletely filled, would increase drastically. Problems in other machines of the packaging line could also require a reduction in the cycle rate.
If the cycle rate R is reduced to a different cycle rate RV to prevent an increased portion of improperly filled blisters, each cycle has a higher maximum cycle time Tmax. If the cycle rate R of 75 cycles per minute is reduced to a different cycle rate RV of 50 cycles per minute, a new maximum cycle rate Tmax=60,000/50=1,200 (ms) is obtained. In a conventional blister packaging machine, the basic behavior of the stored, cycle curve is maintained, with all time periods TV1, TB, TV2 and TR being extended by a factor of 1,200/800=1.5. A correspondingly extended cycle curve is shown in FIG. 3. The figure shows that the duration TB of the treatment, e.g. a forming or cooling process of the bottom sheet is increased by 50%. Moreover, the duration of the first and second adjusting motions is increased in such an extended cycle curve which can reduce the advance speed thereby extending the cooling time of the pre-heated bottom sheet during the transport period. Changing of the process parameters can cause erroneously or incompletely shaped cups.
It is the underlying purpose of the invention to provide a method for controlling a blister packaging machine, wherein the cycle rate can be arbitrarily changed within predetermined limits in the production phase without causing problems during the packaging process and, in particular, during forming of the bottom sheet or during sealing of the cover sheet.